A large body of evidence indicates that monoamine oxidase (MAO) exists in at least two catalytically and immunologically distinct forms. In order to better understand the biology of this pharmacologically important enzyme, the following experiments are proposed: a. MAO will be purified from rat liver (a source for both enzyme forms) to the highest possible degree by using modifications of existing methods. The two forms of the enzyme (MAO A and MAO B) will be resolved by affinity chromatography with a specific inhibitor of MAO A as a ligand. The resulting preparations will be used to produce specific antibodies to the isozymes. b. The antibodies will be used as reagents to determine the hepatic site of biosynthesis of MAO A and MAO B (membrane-bound ribosomes, free ribosomes or mitochondria) with respect to the apoprotein and the flavin cofactor. Using radioactive amino acids, and riboflavin, the turnover rate of each form will be estimated. c. The antibodies will also be used in conjunction with fluorescent antibodies to determine the anatomical localization of these enzyme forms in the rat brain.